The inverted triangle in the structure is the conical antenna. The plane at the bottom is the ground of the antenna.

Le Meins, "A novel broadband eighth-wave conical antenna," IEEE Transactions on Antennas and Propagation, vol.

King, "Input impedance of wide-angle conical antennas fed by a coaxial line," Proceedings of the IRE, vol.

Figure 5 compares the simulated electric field distribution in the radiative near-field region of the circularly polarized

conical antenna with and without the designed GRIN metamaterial lens at 10.5 GHz.

Liu, "A low-profile and broadband

conical antenna," Progress In Electromagnetics Research Letters, Vol.

Truncated versions of the biconical and conical antenna have been addressed as early as the 1940s by Schelkunoff [3], Smith [4] and Papas and King [5, 6], providing analytic approaches to calculate the antenna impedance and field pattern dependence on frequency and on the main geometric parameters (length and flare angle).

Such estimates maybe derived analytically, for instance, when closed-form equations are available, as in the case of the spherically capped conical antenna (SCCA) addressed in [5].

This conical antenna configuration was assessed by Papas and King in [5] to derive an equation of the input impedance [Z.sub.in] of an antenna of length a and flare angle [[theta].sub.0], leading to

In order to introduce the fundamentals of volumetric and planar designs, some features of the well-known biconical antenna and the solid-planar correspondence principle are described in Section 2; Section 3 presents the design process as an evolution of an omnidirectional conical antenna; in Section 4 details of the design of the proposed antenna are given; the derivation of the equation that relates the lower cutoff frequency and the radiator length is shown in Section 5; the prototypes and obtained results for the input impedance bandwidth and the radiation pattern are described in Section 6; finally, in Section 7 the conclusions are formulated.

The design process takes as a basis a single conical antenna on a large flat ground plane and whose input impedance is one-half of the biconical structure [22]:

By following results presented in [23], it is found that a value of a = 90[degrees] provides very low variations on the reactive part of the conical antenna impedance over a very wide range of frequencies and radiator lengths.

Working in concert, the interferometer's three

conical antennas, each 1.2 meters in diameter, act as a three-element radio telescope.